Downloading is possible for both photos and videos from posts, as well as for stories, reels or profile picture.
There was no problem when testing it on my two accounts here. Therefore, it may be that Instagram recently updated and tested the new layout. Please open a new issue on Github, and press the ALT+Z hotkey on the story page to paste the DOM tree in the input box into the Github issue.
https://github.com/SN-Koarashi/ig-helper/
That Dom tree thing is like 500 lines big, it slowed my PC to a crawl when I opened it
I know it's big but this is the only way I can think of to quickly debug it right now...
Posted the DOM on the github
It doesn't seem to be working on stories anymore